Recently, in a cloud service that is realized in a data center or the like, server resources are shared by a lot of customers. Therefore, demands increase to construct a network for directly connecting with a lot of servers as a duplicated broadband network (or network, which is made redundant), which is made by connecting a lot of switches with plural paths.
Because switches in front of the servers are layer-2 switches, a loop is formed when building the aforementioned network as it is. Therefore, Spanning Tree Protocol (STP) or the like might be used. However, in such a case, the redundant path is blocked and cannot be used. Therefore, the network is not broadband. A switch appears, which is called “Fabric switch”, and by which plural same switches are logically integrated, plural connection lines are used as redundant paths by communicating states among the plural same switches, and it is possible to build the duplicated broadband network without using STP. “Fabric” represents a network built by the Fabric switches.
In order to have plural switches logically recognized as one switch, this Fabric switch is desired to have following functions, for example.
(A) Plural paths provided between Fabric switches can be effectively utilized and a loop is avoided.
(B) In order to support a connection (i.e. Link Aggregation (LAG)) in a form that redundancy for outside networks or servers is secured, the Fabric switch supports MLAG (Multi-chassis Link Aggregation. This is a connection in a form that plural lines included in the LAG are connected with different switches.).
(B) can be handled by developing a dedicated relay hardware (e.g. Application Specific Integrated Circuit (ASIC) chip) or using a hardware on the market, which has the MLAG function.
Even when any hardware is employed, state synchronization with hardwares in other switches is performed in order to realize the MLAG function, and the lines between the Fabric switches are not normal lines of Ethernet (Registered Trademark). In other words, the MLAG function is realized by performing communication in a unique format between the Fabric switches through the lines used as internal links. Here, the function for performing communication in the unique format is individually prepared for each hardware, however, in addition to the MLAG function, a function as an internal function is provided in almost all cases to avoid a loop in case where the loop is built with internal connection lines between the hardwares. Therefore, (A) can be resolved by utilizing such a function. However, this solution depends on the internal specification provided by a vendor of the hardware, and the aforementioned function is utilized in a different purpose. Therefore, when an unfavorable result is obtained, correction or change may be difficult.
In addition, in order to realize (A), Transparents Interconnection of Lots of Links (TRILL: RFC5556), Shortest Path Bridge (SPB: IEEE802.1aq) and the like exist presently. Therefore, plural paths can be efficiently utilized by using those techniques. However, when MLAG is realized by the aforementioned hardware, a mechanism for connecting the switches in a unique format is utilized unavoidably, however, it is known that an affinity of such a mechanism with TRILL or SPB is bad.
Moreover, TRILL and SPB add a MAC (Media Access Control) header to an input frame, and control the communication paths by converting the added MAC address Hop by Hop. Because the MAC header is added to the internally relayed frame, an overhead that is longer than 20 Bytes is attached to the input frame received from the outside, and the bandwidth when transferring a short frame (e.g. 64 bytes) is largely reduced. This is because the ratio of the overhead length is great compared with the frame length.
Thus, there is no technique for enabling plural paths provided between first switches and second switches to be effectively utilized.
Patent Document 1: Japanese National Publication of International Patent Application No. 2005-522774
Patent Document 2: Japanese Laid-open Patent Publication No. 11-103302